The Institution of Highways & Transportation (IHT) is grateful for the opportunity to take up your invite and contribute to your document. Having consulted with our members, our comments are as follows:

Observed driver practice over recent years has indicated a steady rise in the average speeds and in all probability in free flow conditions on any part of the motorway network approximately 20% of the traffic (only cars and vans because HGV's are speed limited) exceed the posted speed limit by between 10-15 mph. Drivers, one can only presume, feeling cosseted in a safe environment with in their modern vehicles are prepared to travel at high speeds with short headway distances between leading and trailing vehicles because they have realised there is increasing less likelihood of their poor driving behaviour being observed by police officers. This driving pattern does not appear to be affecting (increasing) the casualty rate but the numbers of deaths on motorways are not falling in the same way that they are on other parts of the road network. A factor in this may be an increasing number of high differential speed impacts which result from these high vehicle speeds.

  Research work undertaken to look into how methods and levels of policing affect road casualty rates by TRL the main findings were as follows:

The great majority of studies in the literature have found that increasing the level of traffic policing reduces the number of road accidents and traffic violations.

  Theory suggests that the relationship between levels of policing and accident/casualty rates is non-linear. At zero enforcement level, accidents and casualties are expected to be at their highest levels. Increases in enforcement will have no noticeable effect at first but at a certain level, when drivers become aware of the increased police presence, accidents and casualties can be expected to begin to fall. Once a saturation point is reached, however, further increases in enforcement levels can be expected to have little or no effect. The challenges for road safety researchers are to establish the levels of policing that are required to bring about the initial decrease in accidents or casualties and to reach the saturation point, and to establish the accident and casualty reductions that can be achieved with these levels of policing.

  Unfortunately, it is difficult in practice to establish the relationship between levels of policing and accident or casualty rates. It has not proved possible to establish the relationship by generalising from studies in the literature because appropriate information about enforcement levels is not given consistently by the different studies. Despite the difficulty of establishing the precise relation between policing levels and accident or casualty rates, some studies have provided limited information about the levels of enforcement required to improve safety. It seems as though stopping one in every six speeding offenders, for example, should have a noticeable effect.

  On the basis of the literature it is also possible to discriminate between stationary and mobile methods of traffic policing. Each method can involve visible policing in either marked or unmarked police vehicles. Stationary and highly visible policing appears to be the most effective method for reducing violations and accidents, although stationary enforcement in unmarked vehicles has also been found to be effective. Mobile policing methods appear less effective, especially when unmarked police vehicles are used.

  The effects of increased stationary enforcement seem to last for a limited amount of time after the police presence has been removed. The largest time "halo" appears to be eight weeks, although sustained police presence is required to produce such large effects. The distance halo of stationary policing appears to be in the range of 1.5 miles to five miles from the enforcement site.

  There is evidence in favour of deploying traffic police largely at random over the whole road network. Theoretically it is likely to increase deterrence. In practice, the random allocation of stationary policing methods to different locations on the road network has been found to be effective, producing substantial impacts on accident rates and reductions in mean speeds and large distance halo effects. The main advantage of this method of traffic policing is that it requires relatively low levels of police manpower.

  Speed cameras have been found to be particularly effective enforcement tools. They appear to be more effective than physical policing methods in reducing mean speeds and accidents. However, physical policing methods have still been found to be effective and the effects of speed cameras appear to be mainly limited to the speed camera site. On the basis of the literature reviewed, the minimum distance halo associated with physical policing is about five times greater than the minimum associated with speed cameras.

  The Institution of Highways and Transportation, founded in 1930, has 10,600 members concerned with the design, construction, maintenance and operation of transport systems and infrastructure across all transport modes in both the public and private sectors. The IHT promotes excellence in transport systems and infrastructure.

19 January 2006